System and method for measuring material added to a vessel under a vacuum

ABSTRACT

The present invention relates generally to weight measurement methods and systems, and more specifically, to weight measurement methods and systems for material in a dynamic vacuum material transfer or other system utilizing differential conveying fluid pressure. The invention determines a corrected weight of a batching tank. The invention includes measuring and logging weights and pressures while the batching tank is being evacuated and determining the density of the air in the batching tank at one or more pressures. While material is being transferred into the vessel the invention measures the weight and pressure of the batching tank and calculates the corrected weight based on logged weights, logged pressures, and the density of the material added to the batching tank.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of co-pending application Ser. No.10/757,860 filed Jan. 15, 2004.

BACKGROUND

The present invention relates generally to weight measurement methodsand systems, and more specifically, to weight measurement methods andsystems for material in a dynamic vacuum material transfer or othersystem utilizing differential conveying fluid pressure.

Shown in FIG. 1 is an example of a dynamic vacuum bulk material transfersystem. Before the batching tank 110 is evacuated, the system operatorzeros a weight measurement device 120 that measures the weight of thebatching tank 110. A vacuum pump 130 is attached to batching tank 110and activated to create a vacuum. After the tank is suitably evacuated,the operator causes material from one or more of the storage tanks 105_(1 . . . N) to be delivered to batching tank 110 by opening acorresponding one of the valves 125 _(1 . . . N). The vacuum pump 130creates a pressure difference in the system. Materials are transferredfrom one of the storage tanks 105 _(1 . . . N) to the batching tank 110by air currents caused by the pressure difference in the system. Afterthe weight of the batching tank 110 has reached a desired weight theoperator will cause the flow of material from the one of the storagetanks 105 _(1 . . . N) to cease by closing the corresponding one of thevalves 125 _(1 . . . N). The operator may continue to add materials tothe batching tank 110 from the storage tanks 105 _(1 . . . N),delivering a desired amount of each material to the batching tank.Thereafter, the operator will shut off the vacuum pump 130. The operatorwill also cause the material in the batching tank 110 to be transferredto the destination vessel 115.

The method described above may cause an inaccurate amount of material tobe delivered to the batching tank 110. This is because the weightmeasurement device 120 is zeroed before the tank is evacuated. While thebatching tank 110 is evacuated, air is removed, lowering the weight ofthe batching tank 110. As material is transferred to the batching tank110, the material fills some volume. As this volume transferredapproaches the volume of the batching tank 110, the weight of thebatching tank 110 and the material in the batching tank 110 approachtheir weight at atmospheric pressure. During filling, however, theweight reported by the weight measurement device 120 is the weight ofthe material in the vacuum, and not the weight of the material atatmospheric pressure. Therefore, there is a discrepancy in the measuredweight of the material during dynamic vacuum material transfer and themeasured weight of the material at atmospheric pressure.

When the operator fills the batching tank 110 with material, he/she willfill the tank until the scale reads the amount of material that isdesired in the tank. The reading of the weight measurement device,however, reflects not only the weight of the material in the tank, butalso the difference between the amount of air initially in the tank andthe amount of air in the evacuated tank. If the batching tank 110 has alarge volume, the vacuum may decrease the weight on the scaledramatically. This process may lead to inaccurate measurement ofmaterial in the batching tank 110. For example, oilfield cement is mixedin a large batching tank 110, so that the weight difference between anevacuated batching tank 110 and unevacuated one may amount to hundredsof pounds.

One way to obtaining the weight of the batching tank 110 at atmosphericpressure involves venting the tank. The batching tank 110 may be ventedafter each material is added to determine the weight of the batchingtank 110 at atmospheric pressure. A drawback of this approach is thatsignificant time is spent venting and then re-evacuating the tank.

Another way of obtaining a more accurate weight of the batching tank 110involves the use of a flow meter. If a flow meter is inserted betweenthe storage tanks 105 _(1 . . . N) and the batching tank 110, the volumeof material transferred can be measured. If the density of the materialis known, the weight of the material transferred to the batching tank110 can be calculated. However, in dry material transfer, a flow meterwill tend to either block the passage between the storage tanks 105_(1 . . . N) and the batching tank 110, or the flow meter may bedestroyed by the material while it passes though the flow meter.

SUMMARY

The present invention relates generally to weight measurement methodsand systems, and more specifically, to weight measurement methods andsystems for material in a dynamic vacuum material transfer or othersystem utilizing differential conveying fluid pressure.

One embodiment of the present invention includes a method fordetermining a corrected weight of a batching tank. The batching tank isadapted to receive one or more materials, each material having adensity. The batching tank has a weight, a pressure, and a volume. Thebatching tank initially includes a fluid having a density. The methodincludes: measuring one or more first weights of the batching tank,wherein the first weights are determined while the fluid is removed fromthe batching tank; logging the first weights; measuring one or morefirst pressures in the batching tank, wherein each first pressure isdetermined substantially simultaneously with the determination of afirst weight; logging the first pressures; measuring one or more secondweights of the batching tank, wherein each second weight is measuredwhile a material is transferred into the batching tank; measuring one ormore second pressures in the batching tank, wherein each second pressureis measured substantially simultaneously with the measurement of eachsecond weight; and determining a corrected weight of the batching tankbased on one of the second weights, one of the second pressures, one ormore first weights, one or more first pressures, the density of thematerial being transferred to the batching tank, and the density of thefluid.

Another embodiment of the present invention includes a method fortransferring material to a batching tank. The material has a density.The batching tank has a weight, a pressure, and a volume. The batchingtank initially includes a fluid having a density. The method includes:removing fluid from the batching tank; measuring one or more firstweights of the batching tank, wherein the first weights are determinedwhile the fluid is removed from the batching tank; logging the firstweights; measuring one or more first pressures in the batching tank,wherein each first pressure is measured substantially simultaneouslywith the measurement of the first weight; logging the first pressures;transferring a material to the batching tank; measuring a second weightof the batching tank, wherein the second weight is measured while thematerial is being transferred into the batching tank; measuring a secondpressure in the batching tank, wherein the second pressure is measuredsubstantially simultaneously with the measurement of each second weight;and determining a corrected weight of the batching tank based on thesecond weight, the second pressure, one or more first weights, one ormore first pressures, and one or more material properties.

Another embodiment of the present invention includes a material transfersystem capable of transferring a material to a batching tank. Thebatching tank has a weight, a pressure, and a volume. The batching tankinitially includes a fluid. The fluid has a density. The material has adensity. The system includes: a vacuum pump, the vacuum pump removeablyconnected to the batching tank and operable to remove fluid from thebatching tank; a weight measurement device operable to measure one ormore first weights of the batching tank and a second weight of thebatching tank, the weight measurement device having an output; apressure measurement device operable to measure one or more firstpressures in the batching tank and a second pressure in the batchingtank, the pressure measurement device having an output; one or morevalves for allowing the material to enter the batching tank, each valvehaving a control input; and a control unit in communication with to theoutput of the weight measurement device and the output of the pressuremeasurement device, the control unit operable to record one or morefirst weights measured by the weight measurement device and one or morefirst pressures measured by the pressure measurement device, the controlunit operable to determine a corrected weight.

The features and advantages of the present invention will be readilyapparent to those skilled in the art upon a reading of the descriptionof the embodiments which follows.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is better understood by reading the followingdescription of non-limitative embodiments with reference to the attacheddrawings wherein like parts of each of the several figures areidentified by the same referenced characters, and which are brieflydescribed as follows:

FIG. 1 is a block diagram of a prior art dynamic vacuum bulk materialtransfer system.

FIG. 2 is a block diagram of a dynamic vacuum bulk material transfersystem in accordance with the present invention.

FIG. 3 is a block diagram of a bulk material transfer system inaccordance with the present invention.

FIG. 4 is a flow chart of a method for dynamic vacuum bulk materialtransfer in accordance with the present invention.

FIG. 5 is a flow chart of a method for dynamic vacuum bulk materialtransfer in accordance with the present invention.

FIG. 6 is a flow chart of a method for dynamic vacuum bulk materialtransfer in accordance with the present invention.

FIG. 7 is a flow chart of a method for bulk material transfer inaccordance with the present invention.

FIG. 8 is a flow chart of a method for bulk material transfer inaccordance with the present invention.

FIG. 9 is a flow chart of a method for bulk material transfer inaccordance with the present invention.

FIG. 10 is a flow chart of a method for calibrating a system inaccordance with the present invention.

It is to be noted, however, that the appended drawings illustrate onlytypical embodiments of this invention and are therefore not to beconsidered limiting of its scope, as the invention may admit to otherequally effective embodiments.

DETAILED DESCRIPTION

The present invention relates generally to weight measurement methodsand systems, and more specifically, to weight measurement methods andsystems for material in a dynamic vacuum material transfer or othersystem utilizing differential conveying fluid pressure. A desirablefeature of the system and method of the present invention is quicker andmore accurate measurement of materials transferred in a vacuum transfermaterial system.

The details of the present invention will now be discussed withreference to the figures. Turning to FIG. 2, a dynamic vacuum materialtransfer system is shown generally by reference to numeral 200. System200 comprises one or more storage tanks 105 _(1 . . . N). Each of thestorage tanks 105 _(1 . . . N) may be of any size or configuration,depending on the application of the system. In one embodiment, thestorage tanks are cylinders, preferably having a twelve foot diameterand thirty-two foot height. The storage tanks may be uniform, or theymay have different dimensions and configurations. For example, if largequantities of one material are used, one of the storage tanks 105_(1 . . . N) holding that material may be larger than the other storagetanks 105 _(1 . . . N). The storage tanks 105 _(1 . . . N) may containmaterials for use in the system 200. The material may be solid orliquid. The material will have properties, including a density. In oneembodiment, the materials stored in the storage tanks are components ofoil field cement. In one example of this embodiment, sand, having adensity of about 100 lbs/ft³, or asphaltum, such as that sold under thetrademark GILSONITE by the American Gilsonite Company of San Francisco,Calif., having a density of about 55 lbs/ft³ may be stored in one of thestorage tanks 105 _(1 . . . N).

The system 200 further comprises one or more valves 125 _(1 . . . N),each valve corresponding to one of the storage tanks 105 _(1 . . . N).Each of the valves 125 _(1 . . . N) is in communication with thecorresponding one of the storage tanks 105 _(1 . . . N). In oneembodiment of the present invention each of the valves 125 _(1 . . . N)is connected to the corresponding storage tank by a pipe or otherconduit that allows material to move from the corresponding storage tankto the valve. Each of the valves 125 _(1 . . . N) is capable of lettingmaterial pass or halting the flow of material from the correspondingstorage tank. The valves may be controlled by an operator of the systemto selectively pass material from the corresponding storage tank. Thevalves may be controlled manually (e.g., with a lever, knob, or othermanual control apparatus) or electronically.

The system 200 further comprises a batching tank 110, which is incommunication with, and adapted to receive material from each of thestorage tanks 105 _(1 . . . N) via valves 125 _(1 . . . N). The batchingtank 10 my be connected to the valves 125 _(1 . . . N) by pipes, hoses,or other conduits suitable for handling the material used in the system200. The batching tank may be of any size or configuration, depending onthe needs of the system. In one embodiment of the present invention, thebatching tank 110 may range from 410 ft³ to 1600 ft³ in volume.

The batching tank 110 is adapted to be connected to a vacuum pump 130.The vacuum pump 130 is used to remove a fluid from the batching tank110. The fluid may be any liquid or gas which is suitable to transportthe material in the dynamic vacuum transfer system. In one embodimentthe fluid comprises air. The vacuum pump 130 may comprise any apparatuscapable of initially lowering the pressure of the batching tank 110 andlater maintaining a dynamic vacuum while material is transferred fromthe storage tanks 105 _(1 . . . N) to the batching tank 110. The vacuumpump 130 is capable of lowering the pressure in the batching tank 110sufficiently to cause a pressured differential in the system, causingmaterial to move from the storage tanks 105 _(1 . . . N) to the batchingtank 110. The magnitude of the pressure differential created by thevacuum pump 130 may vary based on the needs and configuration of thesystem 200. In an exemplary embodiment of the system, the vacuum pump130 is capable of lowering the pressure in the batching tank 110 toabout 5.7 psi (absolute), and maintaining a pressure of about 7.7 psi(absolute) during dynamic vacuum material transfer. The vacuum pump 130may further comprise a control input for controlling the operation ofthe vacuum pump 130, including whether the pump 130 is on or off and howmuch fluid it is evacuating from the batching tank 110.

Turning now to FIG. 3, an alternative embodiment of the system of thepresent invention, represented generally by the numeral 300, isillustrated. The batching tank 110 of the system 300 may be vented. Thesystem comprises one or more pumps 302 _(1 . . . N), each of the one ormore pumps 302 _(1 . . . N) coupled to one or more of the storage tanks105 _(1 . . . N). Each of the pumps 302 _(1 . . . N) may comprise anyapparatus capable of initially raising the pressure of the correspondingstorage tank 105 _(1 . . . N) and later maintaining the pressure whilematerial is transferred from the storage tanks 105 _(1 . . . N) to thebatching tank 110. Each of the pumps ³⁰² _(1 . . . N) may comprise acompressor or a blower. Each of the pumps 302 _(1 . . . N) is capable ofraising the pressure in one of the storage tanks 105 _(1 . . . N)sufficiently to cause a pressured differential in the system, causingmaterial to move from one of the storage tanks 105 _(1 . . . N) to thebatching tank 110. The magnitude of the pressure differential created byeach of the pumps 302 _(1 . . . N) may vary based on the needs andconfiguration of the system. In another embodiment of the presentinvention the system comprises only a single pump 302 ₁ in communicationwith all of the storage tanks 105 _(1 . . . N).

Returning to FIG. 2, the system 200 further comprises a weightmeasurement device 120 for measuring a weight of the batching tank 110.The weight measurement device 120 may comprise any apparatus adapted tomeasure the weight of the batching tank 110. The weight measurementdevice 120 is in communication with the batching tank 110, such that theweight measurement device 120 can measure the weight of the batchingtank 110. In one embodiment, the weight measurement device 120 comprisesa load cell, placed beneath the batching tank 110 to measure the weightof the batching tank 110. The weight measurement device 120 has anoutput for relaying the measured weight.

The system 200 further comprises a pressure measurement device 210 tomeasure the pressure within the batching tank 110. The pressuremeasurement device 210 may comprise any apparatus capable of measuringthe pressure within the batching tank 110. The pressure measurementdevice 210 is situated so that it can measure the pressure within thebatching tank 110. The pressure measurement device 210 has an output fortransmitting the pressure within the batching tank 110.

The system 200 further comprises a control unit 205. The control unit205 may comprise one or more computers or other apparatuses. The controlunit 205 may be in communication with and adapted to control, the valves125 _(1 . . . N) and the vacuum pump 130. The control unit 205 comprisesa weight input in communication with the output of the weightmeasurement device 120 and a pressure input in communication with theoutput of the pressure measurement device 210. The control unit 205 maybe in communication with, and adapted to control, the valves 125_(1 . . . N). The control unit 205 may be in communication with, andadapted to control, the vacuum pump 130. The control unit 205 is capableof receiving inputs from the weight sensor 120 and the pressure sensor210 and recording the weight and pressure measurements. The control unit205 may be an integrated computer control system comprising one or moreinputs (e.g. keyboard, mouse, input ports for communicating with theweight measurement device 120 and the pressure measurement device 210),one or more outputs (e.g. CRT, LCD, printer, or ports for communicatingwith the inputs of the valves 125 _(1 . . . N)), one or more processors,and a memory.

Referring again to FIG. 3, in system 300 shown in FIG. 4, the controlunit 205 is in communication with, and adapted to control the pumps 302_(1 . . . N). If the system 300 comprises only a single pump 302 ₁, thecontrol unit is in communication with, and adapted to control the pump302 ₁.

Returning now to FIG. 2, the system 200 further comprises a destinationvessel 115. The destination vessel 115 is adapted to receive materialfrom the batching tank 110. The batching tank 110 may comprise a vesselof suitable dimensions and arrangement to hold the material transferredfrom the batching tank 110. In one embodiment of the present invention,the destination vessel 115 may comprise a truck with a tank or otherreceptacle for hauling oilfield cement.

Turning now to FIG. 4, a method of operation of the system 200 accordingto the present invention will be described. The method starts at block401 and proceeds to block 405, where fluid is removed from the batchingtank 110 by the vacuum pump 130, creating a vacuum, and the method thenproceeds to block 410. In one embodiment, the control unit 205 causesthe vacuum pump 130 to activate.

In block 410, a first pressure of the batching tank 110 and a firstweight of the batching tank 110 are measured and these measurements arelogged while the batching tank 110 is being evacuated. The method maytake continuous readings. Alternatively, the method may only log thepressure and weight of the tank at some time interval, e.g. everysecond; at some pressure interval, e.g. every time the pressure in thetank drops one psi; or, at some weight interval, e.g. every time theweight of the tank drop one pound. In one embodiment, the control unit205 records the pressure within the batching tank 110 and the weight ofthe batching tank 110 every time the pressure within the batching tank110 drops about one psi. Preferably, each set of corresponding weightand pressure measurements are made substantially simultaneously. Afterthe weight of the batching tank 110 and the pressure in the batchingtank 110 are measured and possibly logged the method proceeds to block415. In block 415, the control unit 205 determines if the tank issuitably evacuated by comparing the first pressure with an evacuatedpressure. The evacuated pressure may be a constant stored by the controlunit 205, or it may be entered by the operator. If the first pressure isless than or equal to the evacuated pressure, the method will proceed toblock 420. If the first pressure is greater than the evacuated pressurethe method will return to block 405. In block 420, the method fills thebatching tank 110 with one or more materials. After the method isfinished filling the batching tank 110 with the one or more materials itproceeds to block 425, where it ends.

Referring now to FIG. 5, block 420, in which the method of the presentinvention fills the batching tank 110, is shown in greater detail. Themethod begins at block 505. The method proceeds to block 510, where aprevious weight is set to zero. In block 515 the method causes thebatching tank 110 to be filled with a next material. In block 535, themethod determines if the batching tank is suitably filled with a currentmaterial. If the batching tank 110 is finished filling with the one ormore materials the method proceeds to block 550, where the method ends.If the batching tank 110 is not finished filling with the one or morematerials the method proceeds to block 545. In block 545, the methodincrements the previous weight by a corrected weight of the batchingtank 110.

Referring now to FIG. 6, block 515, in which the batching tank is filledwith a next material is shown in greater detail. The method starts atblock 605 and proceeds to block 610 where the batching tank 110 isfilled with the current material. In one embodiment of the presentinvention, the control unit 205 operates one of the valves 125_(1 . . . N), causing it to open, thus allowing material from one of thestorage tanks 105 _(1 . . . N) to move into the batching tank 110. Inanother embodiment, the operator of the system manually operates one ofthe valves 125 _(1 . . . N). In block 615 the method measures a secondweight of the batching tank 110 and a second pressure in the batchingtank 110. In one embodiment, the control unit 205 receives the secondweight from the weight measurement device 120 and the second pressurefrom the pressure measurement device 210. Alternatively, the readingsfrom the weight measurement device 120 and the pressure measurementdevice 210 may be taken manually by the operator.

In block 620 the method determines the corrected weight of the batchingtank 110. In one embodiment, the control unit 205 determines thecorrected weight of the batching tank 110. The control unit 205 may usethe following relationship to determine the corrected weight of thebatching tank 110: $\begin{matrix}{{W_{I} = {{\sum\limits_{0}^{n}W_{{act}_{n}}} - \quad{\left\lbrack {V_{TK} - {\sum\limits_{0}^{n}\frac{W_{act}}{\rho_{{act}_{n}}}}} \right\rbrack\left( {\rho_{{gas}_{0}} - \rho_{{gas}_{current}}} \right)}}},} & \left( {{Equation}\quad 1} \right)\end{matrix}$In Equation 1, W₁ is the weight measured by the weight measurementdevice 120, n is the number of materials added to the batching tank 110,W_(act) _(n) is an actual weight of the n^(th) material added to thebatching tank 110, V_(TK) is a volume of the batching tank 110, ρ_(act)_(n) is a density of the n^(th) material added to the batching tank 110,ρ_(gas) ₀ is a density of the fluid at atmospheric pressure, ρ_(gas)_(current) is a density of the fluid at the second pressure. Therelationship may be solved for W_(act) _(n) by one skilled in the artwith the benefit of this disclosure. The volume of the batching tank 110may be stored in the control unit 205 as a constant, or it may beentered by the operator. The density of each of the n materials may bestored in the control unit 205 as constants or the densities may beentered by the operator. If the control unit 205 is operating the valves125 _(1 . . . N) and knows the densities of the materials, then it canselect the density for the n^(th) material automatically. The density ofthe fluid at atmospheric pressure can be determined by the measurementsof the first weights taken while the batching tank 110 was beingevacuated. For example, the control unit 205 may divide the firstweight, recorded while the batching tank 110 was at atmosphericpressure, by the volume of the batching tank 110. Alternatively, thedensity of the fluid at atmospheric pressure may be stored by thecontrol unit 205 as a constant or entered by the operator. The densityof the fluid at the second pressure may be determined by themeasurements of first weights and first pressures, measured and recordedwhile the batching tank 110 was being evacuated.

In one embodiment, the control unit 205 may select the correspondingfirst weight and first pressure, where the first pressure is closest tothe second pressure. Then, the control unit may divide the correspondingfirst weight by the corresponding first volume of the batching tank 110to determine the density of the fluid at the second pressure.Alternatively, the control unit 205 may perform an interpolation of therecorded first weights and first pressures, producing a series ofinterpolated first weights and corresponding interpolated firstpressures. This interpolation may use a straight line method, a leastsquares method, or another method, depending on the behavior of thesystem and the needs of the operator. The control unit 205 may thenselect an interpolated first weight, where the interpolated first weightcorresponds to the interpolated first pressure that is closest to thesecond pressure. Then, the control unit may divide the correspondinginterpolated first weight by the volume of the batching tank 110 todetermine the density of the fluid at the second pressure. Afterdetermining the corrected weight, the method proceeds to block 625.

In block 620, the method may also calculate the corrected weight of thebatching tank 110 without references to the first weights and firstpressures. Rather, the method may use dynamic or steady-state fluidrelationships to determine the density of the gas as the secondpressure, and then solve for the corrected weight of the batching tank110. An example equation that may be employed by the method is:PV=mRT  (Equation 2)Where P is the second pressure, V is the volume occupied by the fluid, mis the mass of the fluid in the batching tank 110 in number of moles, Ris a constant (often referred to as a Universal Gas Constant) based onthe units of measurement, and T is the temperature within the batchingtank 110, which may be measured by a temperature measurement device,input by the operator, or assumed. One of ordinary skill in the art,with the benefit of this disclosure can solve for the density of thefluid based on Equation 2.

In block 625, the method determines if the corrected weight less theprevious weight is greater than or equal to a target weight. The targetweight may be stored in the control unit 205 as a constant or may beentered by the operator. If the corrected weight less the previousweight is not greater than or equal to the target weight the methodproceeds to block 630, where the method continues to fill the batchingtank 110 with the current material and returns to block 615. If thecorrected weight less the previous weight is greater than or equal tothe target weight the method proceeds to block 635 where the methodstops filling the batching tank 110 with the current material andproceeds to block 640 where the method ends.

In block 635 the method will halt the flow of material to the batchingtank 110. This may be accomplished by the control unit 205 closing allof the valves 125 _(1 . . . N) that are open by sending a control signalto the valves 125 _(1 . . . N). Alternatively, the operator may manuallyclose the valves 125 _(1 . . . N) that are open. Additionally, themethod may transfer the material in the batching tank 110 to thedestination vessel 115.

Turning now to FIG. 7, a method of operation of the system 300 accordingto the present invention will be described. The method starts at block705 and proceeds to block 710, where the batching tank 110 is vented. Inblock 715 the method of the present invention causes one or more of thestorage tanks 105 _(1 . . . N) to be pressurized. In block 720 themethod of the present invention fills the batching tank 110 with one ormore materials from one or more of the storage tanks 125 _(1 . . . N).In block 725 the method of the present invention ends.

Referring now to FIG. 8, block 720, in which the method of the presentinvention fills the batching tank 110, is shown in greater detail. Themethod begins at block 805. The method proceeds to block 810, where aprevious weight is set to zero. In block 815 the method causes thebatching tank 110 to be filled with a next material. In block 820, themethod determines if the batching tank is suitably filled with a currentmaterial. If the batching tank 110 is finished filling with the one ormore materials the method proceeds to block 825, where the method ends.If the batching tank 110 is not finished filling with the one or morematerials the method proceeds to block 830. In block 830, the methodincrements the previous weight by the measured weight of the batchingtank 110.

Referring now to FIG. 9, block 815, in which the method of the presentinvention fills the batching tank 110 with the next material, is shownin greater detail. The method starts at block 905 and proceeds to block910 where the batching tank is filled with the current material. In oneembodiment of the present invention, the control unit 205 operates oneor more of the valves 125 _(1 . . . N), causing them to open, thusallowing material from one or more of the storage tanks 105 _(1 . . . N)to move into the batching tank 110. The control unit 205 may alsooperate one or more of the pumps 302 _(1 . . . N), causing one or moreof the pumps to pressurize one or more of the storage tanks 105_(1 . . . N), forcing material stored in the pressurized storage tanksto move into the batching tank 110. In another embodiment, the operatorof the system manually operates one or more of the valves 125_(1 . . . N). In block 920, the method determines if the measured weightless the previous weight is greater than or equal to the target weight.The target weight may be stored in the control unit 205 as a constant ormay be entered by the operator. If the corrected weight less theprevious weight is not greater than or equal to the target weight themethod proceeds to block 925, where the method continues to fill thebatching tank 110 with the current material and returns to block 915. Ifthe corrected weight less the previous weight is greater than or equalto the target weight the method proceeds to block 930 where the methodstops filling the batching tank 110 with the current material andproceeds to block 935 where the method ends.

In block 930 the method will halt the flow of material to the batchingtank 110. This may be accomplished by the control unit 205 closing theone of the valves 125 _(1 . . . N) that is open by sending a controlsignal to the valves 125 _(1 . . . N). Alternatively, the operator maymanually close the one of the valves 125 _(1 . . . N) that is open. Thecontrol unit 205 may also operate one of the pumps 302 _(1. . . N),causing the pumps 302 _(1 . . . N) to stop pressurizing the storagetanks 105 _(1 . . . N). Additionally, the method may transfer thematerial in the batching tank 110 to the destination vessel 115.

Turning now to FIG. 10, a method of calibration of the system 200according to the present invention will be described. The method startsat block 1005 and proceeds to block 1010, where the method estimates theweight of the batching tank 110 at a series of pressures based onassumptions, operator inputs, and equations such as Equations 1 and 2described above. In block 405 (as described with respect to FIG. 4), themethod evacuates the batching tank 110. In block 415 the methoddetermines if the pressure in the batching tank 110 is less than orequal to the evacuated pressure, as described with respect to FIG. 4. Ifthe pressure in the batching tank 110 is less than or equal to theevacuated pressure the method proceeds to block 710. If the pressure inthe batching tank 110 is greater than the evacuated pressure the methodreturns to block 405. In block 1015, the method of the present inventionvents the batching tank 110. The control unit 205 may open vents on thebatching 110 to vent the batching tank 110. In block 1020 the methodmeasures the pressure and weight of the batching tank 110. The controlunit 205 may obtain the weight measurement from the weight measurementdevice 120 and the pressure from the pressure measurement device 210. Inblock 1025 the method compares the measured pressures and weights withthose calculated in block 1010. If the estimated weight at the measuredpressure is not equal to the measured weight at the measured pressure,the control unit 205 may adjust the calibration of the weightmeasurement device 120 or other portions of the system 200 so that theestimated weight at the measured pressure will equal the measured weightat the measured pressure. In block 1030 the method determines if thebatching tank is fully vented. The control unit 205 may determine if thebatching tank 110 is fully vented by comparing the measured pressurewith atmospheric pressure. If the measured pressure is below atmosphericpressure the control unit will determine that the batching tank 110 isnot fully vented. If the batching tank 110 is fully vented the methodproceeds to block 1035, where it ends.

Therefore, the present invention is well adapted to carry out theobjects and attain the ends and advantages mentioned as well as thosethat are inherent therein. While numerous changes may be made by thoseskilled in the art, such changes are encompassed within the spirit ofthis invention as defined by the appended claims.

1. A material transfer system for transferring a material to a batchingtank, the batching tank having a weight, a pressure, and a volume, thebatching tank initially comprising a fluid, the fluid having a density,the material having a density, the system comprising: a vacuum pump, thevacuum pump removeably connected to the batching tank and operable toremove fluid from the batching tank; a weight measurement deviceoperable to measure one or more first weights of the batching tank and asecond weight of the batching tank, the weight measurement device havingan output; a pressure measurement device operable to measure one or morefirst pressures in the batching tank and a second pressure in thebatching tank, the pressure measurement device having an output; one ormore valves for allowing the material to enter the batching tank, eachvalve having a control input; and a control unit in communication withthe output of the weight measurement device and the output of thepressure measurement device, the control unit operable to record one ormore first weights measured by the weight measurement device and one ormore first pressures measured by the pressure measurement device, andthe control unit operable to determine a corrected weight.
 2. Thematerial transfer system of claim 1 wherein the control unit is operableto: receive one or more first weights from the weight measurementdevice; receive one or more first pressures from the pressuremeasurement device; operating one of the valves, causing material to betransferred to the batching tank; receive a second weight from theweight measurement device, wherein the second weight is determined whilematerial is being transferred into the batching tank; receive a secondpressure from the pressure measurement device, wherein the secondpressure is measured substantially simultaneously with measurement ofthe second weight; and determine a corrected weight based on the secondweight, the second pressure, one or more first weights, one or morefirst pressures, and one or more material properties.
 3. The materialtransfer system according to claim 2 wherein the control unit isoperable to: determine a volume occupied by the fluid; determine avolume occupied by the material; determine a fluid weight by multiplyingthe volume occupied by the fluid by the density of the fluid; determinea material weight by multiplying the volume occupied by the material bythe density of the material; and determine the corrected weight byadding the material weight and the fluid weight.
 4. The materialtransfer system according to claim 2 wherein the control unit isoperable to: select a first weight, wherein the first weight wasmeasured substantially simultaneously with the closest first pressure,and wherein the closest first pressure is nearest the second pressure;and calculate the density of the fluid by dividing the selected firstweight by the volume of the batching tank.
 5. The material transfersystem according to claim 2 wherein the control unit is operable toclose one of the valves to halt material from flowing into the batchingtank.
 6. The material transfer system according to claim 5 wherein thecontrol unit is operable to close one of the valves to halt the flow ofmaterial when the corrected weight is near a target weight.
 7. Thematerial transfer system according to claim 2 wherein the control unitis operable to: log the one or more first weights, wherein each firstweights are measured while the fluid is removed from the batching tank;and log the one or more first pressures, wherein each first pressure ismeasured substantially simultaneously with the measurement of the firstweight.